W123 Wierdness - PeachParts Mercedes-Benz Forum

elcaBob · #1 12-13-2022, 09:54 AM

Hello, all. My 85 300D has started some odd behavior. It’ll be running along just fine and then, suddenly, can’t get out of its own way. I have to practically bury the pedal just to keep it running and it won’t rev up at all. Then, just as suddenly, it clears up and I drive on.

I have to pull over when this starts and it takes 30-90 seconds to straighten out.

Bad gas?
Clogged filters?
Sunspots?

Thanks!
Bobby

WagonTree · #2 12-13-2022, 10:02 AM

Have you noticed this issue travelling uphill and with less than half a tank of fuel? My issue was similar if so, proved to be a fuel lift pressure issue (clogged tank strainer starving IP of fuel).

elcaBob · #3 12-13-2022, 10:25 AM

I have not noticed that it’s only uphill, but I do only have a quarter tank of gas. Thanks!

psaboic · #4 12-13-2022, 10:37 AM

Well, since you only have a quarter tank of (dear God I hope not gas.....) I would take the opportunity to drain the remainder out, and clean the tank strainer. Then I would change all the fuel filters, fill and prime with fresh fuel and see if that helps. Another question....when you remove the fuel cap to add fuel, do you hear a "whoosh" sound of air? If so, your tank vent is clogged and could easily cause your issue. I'm betting on filters though, but either way, draining the tank and cleaning the strainer and cleaning the tank vent are pretty well documented in other threads on the forum....Good luck and let us know the outcome.

elcaBob · #5 12-13-2022, 03:24 PM

I had not considered the vent. Ordering the filters today. And, no, it's not gasoline, but diesel. On the filters, not ONE local parts store even has them available for order. I now HAVE to buy them online. Grrrr.

elcaBob · #6 12-14-2022, 01:39 PM

OK, added some clean fuel and a big bottle of Diesel Kleen and cleared it right up. I'll clean the tank out at some point. I'm going to post separately asking the best way to clean the tank without removing it.

Thanks, All.

Diesel911 · #7 12-14-2022, 03:12 PM

Quote:

Originally Posted by elcaBob

OK, added some clean fuel and a big bottle of Diesel Kleen and cleared it right up. I'll clean the tank out at some point. I'm going to post separately asking the best way to clean the tank without removing it.

Thanks, All.

Startron for diesels is claims it has an enzyme action that eats up stuff and breaks it down small enough to pass through the filters.

On a W123 the tank vent opening is in front of the left rear fender well. Typically, that area can get packed with mud and block the tank vent opening which has a rubber sort of valve on it.

JohnLeCar · #8 12-15-2022, 12:55 AM

Encountered a similar issue once on my w116.
Went with Sun spots at the time.

In all honesty, likely an intermittent vac leak.

Diesel911 · #9 12-15-2022, 12:16 PM

This is the ad from startron.

"Description
Star Tron Enzyme Fuel Treatment is a multi-functional fuel additive which uses a unique enzyme technology that allows all engines to start easily and run smoothly, even after sitting idle for months.

Star Tron® eliminates and prevents fuel problems. Star Tron breaks down excess water and sludge to sub-micron size, allowing it to be safely burned away during normal engine operation.

Star Tron was rated “Best Choice” in an independent review of the seven most popular diesel treatments that guard against fuel-tank corrosion.

Star Tron® increases fuel economy by cleaning the entire fuel delivery system, removing performance robbing gum, and varnish deposits while modifying how fuel burns. This results in more complete and uniform combustion, maximum performance, increased fuel efficiency, reduced emissions, and reliable operation. Star Tron eliminates carbon build-up from burners, injectors, and exhaust components.

Star Tron will stabilize fuel for up to two years, preventing the formation of gums and other solids that clog fuel injectors. Star Tron can help rejuvenate old and sub-spec fuel."

If you decide to use it be sure to get the one for diesel engines.

Star Tron Enzyme Fuel Treatment Diesel Additive

Diesel911 · #10 12-15-2022, 12:21 PM

Since it was mentioned that the spin-on fuel filter is hard to find at regular auto part stores it can be a good idea to keep one in the trunk of the car. I mean you can get a bad load of fuel and it pretty quickly can plug up filters.

People have also said that if you get fuel with a lot of bio-diesel fuel mixed in it that it will clean your tank and fuel system and to have extra filters for that eventuality.

Diesel911 · #11 12-15-2022, 12:24 PM

Since it was mentioned that the spin-on fuel filter is hard to find at regular auto part stores it can be a good idea to keep one in the trunk of the car. I mean you can get a bad load of fuel and it pretty quickly can plug up filters.

People have also said that if you get fuel with a lot of bio-diesel fuel mixed in it that it will clean your tank and fuel system and to have extra filters for that eventuality.

vwnate1 · #12 12-16-2022, 10:36 AM

Startron does indeed work well .

However, in bad cases of fungus infestation it may take seemingly forever to do the job .

For this reason I switched to BioBor as suggested in this forum .

It killed the fungus in two tanks full without needing to remove the tank for external cleaning .

In all cases care should be taken to only use the clear plastic fuel intake screen so you'll have plenty of advance notice before the car starts running poorly .

Mark123 · #13 12-16-2022, 09:03 PM

Something similar happened to my 240D a couple years ago. While it was acting up, I pulled the vacuum line off the shut off on the injection pump. Problem gone. Of course I then had to figure out how I had mis-connected vacuum lines to provide vacuum to the shut off with the key on.